The overall goal of the proposed studies is to examine the correlation between the in vitro antigen presenting capacity and the in vivo capacity of various lipopeptide formulations and CDNA constructs to elicit HLAA2.1 -restricted CTL responses. The data will provide useful information regarding the mechanisms involved in antigen processing of specific HIV-1 vaccine candidates and in evaluating the merit of using in vitro presentation assays as a tool for vaccine optimization and for measuring the potency of vaccine preparations. Specifically, the applicants are interested in an epitope-based approach to therapy and prophylaxis of HIV infection. To this end, the applicants have identified several A2-restricted conserved HIV epitopes and alternative vaccine constructs (lipopeptide cocktails and minigene CDNA) capable of eliciting specific CTL responses in HLA-A2 transgenic mice. For both types of vaccine, the preliminary evidence point to a cell of phagocytic nature as being responsible for in vivo immunogenicity. The applicants plan to generate different lipopeptide formulations and different minigene constructs which vary in their capacity to be processed and presented by antigen presenting cells (APCs). The applicants will then test these formulations and constructs using as APCS, B-cell, T-cell, and macrophage lines, to identify the presenting cell population(s) which are capable of processing and stimulating T cells. Finally, the different formulations and constructs will be tested for their immunogenicity in HLA-A2.1/kb transgenic mice to correlate their activity observed in in vitro presentation assays. Due to the slow sample throughput, high response variability, and laboriousness of animal assays, it would be advantageous to develop a highly correlative in vitro potency assay. The applicants believe that if the in vitro and in vivo activity correlations are observed in their studies, the in vitro APC assay system would offer the following advantages: 1) it will serve as basis for fundamental studies on the mechanisms of antigen processing and vaccine efficiency; 2) it will allow for rapid optimization of different vaccine constructs,; and 3) it will provide a rational potency assay to assist in vaccine development.